The leakage of lubricant out of a bearing is advantageously kept as low as possible in order to ensure that a desired amount of lubricant remains within the bearing. If uncontrolled leakage occurs, the level of lubricant within the bearing could become low. If a bearing is operated at low level of lubricant, detrimental damages may be the consequence for the bearing due to wear and fatigue.
In addition, an elevated rate of leakage of lubricant may lead to additional service costs due to increased service activities of cleaning and filling up the lubricant containers at the wind turbine. In particular, leakage of lubricant on offshore wind turbines may lead to significantly elevated service costs.
Typically, bearings of a wind turbine are sealed such that the amount of lubricant which is leaking out on a regular basis is minimized. Ideally, no or only very little lubricant leaks out of the sealed bearing of the wind turbine. In practice, it may occur, though, that elevated amounts of lubricant may leak out of the bearing. This is attributed at least partially to an overpressure inside the bearing compared to the pressure of the surrounding ambient. Overpressure inside the bearing may be caused by an elevated temperature inside the bearing compared to the ambient. To give an example, if the temperature of a bearing with a bearing diameter of four meters rises from 15 degrees Celsius to 55 degrees Celsius, the pressure inside the bearing might increase by 0.14 bar. In order to reduce the over pressure of inside the bearing compared to the pressure of the ambient, approximately eight liters of air needs to be released from the bearing.
It has been shown that even a relatively small overpressure inside the bearing, e.g. 0.1 bar, may over time lead to significant leakage. This may be the case by slowly pressing the lubricant below the seal lip of such a sealed bearing. Elevated overpressure inside the bearing, e.g. 0.2 bar or higher, may even lead to a significant leakage of lubricant in relatively short time.
In the state of the art, this leakage of lubricant has typically been accepted. In order to minimize the amount of leakage, the overpressure inside the bearing has been tried to minimize.
Thus, there exists the desire of providing an improved concept of reducing the leakage of lubricant out of a bearing of a wind turbine.